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Ultraviolet (UV) absorbents and industrial antioxidants are two groups of plastic-derived contaminants of emerging environmental concern. However, their distribution and fate are poorly understood in Arctic wildlife. In the present study, 16 UV absorbents (10 benzotriazole UV stabilizers (BZT-UVs) and 6 organic UV filters (UVFs)) and 7 industrial antioxidants (6 aromatic secondary amines (Ar-SAs) and 2,6-di-tert-butylphenol (26DTBP)) were analyzed in the livers of thick-billed murre (Uria lomvia; n = 28), northern fulmar (Fulmarus glacialis; n = 4), black guillemot (Cepphus grylle; n = 11), polar bear (Ursus maritimus; n = 18), beluga whale (Delphinapterus leucas; n = 10), landlocked (n = 25) and sea-run (n = 10) Arctic char (Salvelinus alpinus) from the Canadian Arctic collected between 2017 and 2021. Compared to industrial antioxidants (median range: ΣAr-SAs: not calculated due to detection frequency < 30 % (NA)-4.06 ng/g, wet weight (ww); 26DTBP: NA-1.91 ng/g ww), UV absorbents (median range: ΣBZT-UVs: NA-8.71 ng/g ww; ΣUVFs: NA-48.3 ng/g ww) generally showed greater concentrations in the liver of these species. Seabirds accumulated higher levels of these contaminants (median range: ΣBZT-UVs: 3.38-8.71 ng/g ww; ΣUVFs: NA-48.3 ng/g ww; ΣAr-SAs: 0.07-4.06 ng/g ww; 26DTBP: NA-1.14 ng/g ww)) than the other groups (median range: ΣBZT-UVs: NA-1.31 ng/g ww; ΣUVFs: NA-4.22 ng/g ww; ΣAr-SAs: NA; 26DTBP: NA-1.91 ng/g ww), suggesting that seabirds may be useful indicator species for future long-term monitoring. The livers of Arctic char in the Canadian Arctic generally contain lower levels of these contaminants than those of freshwater fish in temperate regions. Spatial variations were found in the liver of black guillemots, Hudson Bay polar bears, and landlocked char for some target contaminants, indicating differences in the levels of these contaminants in their surrounding environment or diet. Consumption of liver tissues from these species may expose humans to varying levels of UV absorbents and industrial antioxidants. This study establishes a baseline for future research of the spatial and temporal trends of these contaminants in Arctic species. It provides the basis for elucidating the fate of these contaminants and assessing their adverse effects at environmental-relevant concentrations in the Arctic. Factors influencing the accumulation patterns of these contaminants in Arctic biota and their potential health risks require further investigation., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

Lake Hazen, the largest lake north of the Arctic circle, is being impacted by mercury (Hg) pollution and climate change. The lake is inhabited by two morphotypes of land-locked Arctic char (Salvelinus alpinus), a sensitive indicator species for pollution and climatic impacts. The objectives of this study were to describe the trends in Hg concentration over time and to determine the relationship of climate to length-at-age and Hg concentrations in each char morphotype, as well as the relationship to atmospheric Hg measurements at a nearby monitoring station. Results for Hg in char muscle were available from 20 sampling years over the period 1990 to 2021. We found significant declines in Hg concentrations for both morphotypes during the 31-year study period. Increased rain and earlier freeze-up of lake ice during the summer growing season was linked to increased length-at-age in both char morphotypes. For the large morphotype, higher total gaseous Hg in the fall and winter seasons was related to higher concentrations of Hg in char, while increased glacial runoff was related to decreases in char Hg. For the small morphotype char, increased snow and snow accumulation in the fall season were linked to declines in char Hg concentration. The Atlantic Multidecadal Oscillation and Arctic Oscillation were positively related to the large char Hg trend and Arctic Oscillation was positively related to the small char Hg trend. Significant trend relationships between atmospheric Hg and Hg in biota in remote regions are rare and uniquely valuable for evaluation of the effectiveness of the Minamata Convention and related monitoring efforts., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper, (Copyright © 2023. Published by Elsevier Ltd.)

Nature archives record atmospheric mercury (Hg) depositions from directly emitted Hg and re-emitted legacy Hg. Tracing the legacy versus newly deposited Hg is still, however, challenging. Here, we measured Hg isotope compositions in three dated sediment cores at different distances from the Flin Flon smelter, the largest Canadian Hg sources to the atmosphere during the 1930s-2000s. During the smelter's operative period, Hg isotope compositions showed limited variations in the near-field lake (<10 km) sediments but were rather variable in middle- (20-75 km) and far-field lake (∼800 km) sediments. Only the post-2000 sediments in middle/far-field lakes showed significantly negative Hg isotope shifts, while sediments from the 1970s-1990s had Hg isotope values resembling those of near-field lake post-1930 sediments. We suggest that the smelter's peak Hg emissions during the 1970s-1990s, which coincided with the deployment of a super stack in the mid-1970s, largely increased the long-range dispersion of smelter plumes. For the top post-2000 sediments, the fugitive dust from ore tailings and terrestrial legacy Hg re-emissions dominated Hg deposition in near-field lakes and middle/far-field lakes, respectively. Our study demonstrates that legacy Hg remobilization now exports substantial amounts of Hg to ecosystems, highlighting the need for aggressive remediation measures of Hg-contaminated sites.

Mercury (Hg) is a pollutant of concern across Canada and transboundary anthropogenic Hg sources presently account for over 95% of national anthropogenic Hg deposition. This study applies novel statistical analyses of 82 high-resolution dated lake sediment cores collected from 19 regions across Canada, including nearby point sources and in remote regions and spanning a full west-east geographical range of ∼4900 km (south of 60°N and between 132 and 64°W) to quantify the recent (1990-2018) spatial and temporal trends in anthropogenic atmospheric Hg deposition. Temporal trend analysis shows significant synchronous decreasing trends in post-1990 anthropogenic Hg fluxes in western Canada in contrast to increasing trends in the east, with spatial patterns largely driven by longitude and proximity to known point source(s). Recent sediment-derived Hg fluxes agreed well with the available wet deposition monitoring. Sediment-derived atmospheric Hg deposition rates also compared well to the modeled values derived from the Hg model, when lake sites located nearby (<100 km) point sources were omitted due to difficulties in comparison between the sediment-derived and modeled values at deposition "hot spots". This highlights the applicability of multi-core approaches to quantify spatio-temporal changes in Hg deposition over broad geographic ranges and assess the effectiveness of regional and global Hg emission reductions to address global Hg pollution concerns.

We investigated the spatio-temporal trends of polycyclic aromatic compounds (PACs) deposition in the Athabasca Oil Sands Region (AOSR) between 2008 and 2017, and applied source apportionment tools to assess sources using snowpacks. Estimated PAC mass deposition was significantly correlated with crude oil production (R 2  = 0.48, p = 0.03), and increased between 2008 and 2017. Loadings of alkylated PACs c1-, c2-fluorenes/pyrenes and c1-, c3-benzo[a]anthracenes/chrysenes/triphenylenes significantly increased at mid-field sites (25-50 km from central industrial reference site, AR6) (Mann-Kendall, p < 0.05) reflecting physical expansion of the AOSR. The distance from emission sources was important in the deposition of PACs, including the distance from AR6 (R 2  = 0.69-0.91), nearest petcoke storage (R 2  = 0.77-0.88), 0.89) and upgrader stack (R 2  = 0.56-0.61). Source apportionment PAC distribution profiles of the source materials (petcokes, oil sand ores, road dust) did not show unique matching profiles with the snowpacks. However, the minimal presence of retene in petcokes and an abundance of benzo[ghi]fluoranthene in road dust was observed, and suggests potential for these compounds as chemical markers in distinguishing sources. Furthermore, correlations between PACs and selected metal(loid)s in the AOSR snowpacks were assessed to infer potential common sources. Significant positive (p < 0.05) correlations between metal(loid)s enriched in bitumen (vanadium, molybdenum, nickel) and PACs, at near to mid-field (0-50 km from AR6) sites suggests common sources or similar transfer and fate processes. The results of our study convey data necessary for monitoring studies in the constantly developing AOSR, advance our knowledge of PACs profiles in source materials (including the much less studied alkylated PACs and dibenzothiophenes), which will be valuable for other studies related to oil pollution, urban run-off and forest fires. PACs mass deposition increasing between 2008 and 2017 coincident with crude oil production, and retene and benzo[ghi]fluoranthene show potential in distinguishing AOSR sources., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Crown Copyright © 2020. Published by Elsevier Ltd. All rights reserved.)

National and global inventories of anthropogenic trace element emissions to air is a comparatively recent phenomenon (post-1993 in Canada) as is the monitoring of atmospheric metal deposition, the latter being also very spatially limited. Paleo-reconstructive methods offer a contiguous record of environmental contamination providing a needed framework to establish locally relevant "pre-industrial" (~natural) conditions which can be compare with relative and quantitative deviations away from reference conditions. In this study, we reconstruct the history of the long-range, anthropogenic sourced atmospheric trace element deposition to the remote region of Northwestern Ontario Canada (Experimental Lakes Area (ELA)) using dated sediment records from five lakes. Several elements are shown to be highly enriched in lake sediments relative to pre-1860 sediments (Antimony, Lead, Tellurium, Tin, Arsenic, Bismuth, Cadmium and Mercury) and moderately (Zinc, Tungsten, Thallium, Copper, Silver, Selenium, Nickel and Vanadium). Mean decadal anthropogenic atmospheric fluxes (mg m-2 yr-1) are reconstructed for 1860-2010 and compare well with available local (ELA), regional (NW Ontario Canada, N Michigan USA) monitoring data, as well as global assessments of anthropogenic contribution to atmospheric trace metal burdens. Quantitative paleo reconstructions of atmospheric contamination history using the collective signal from multiple lakes provide a rigorous methodology to assess trends, uncertainties, evaluation with monitoring data and, provide an opportunity to explore landscape processes of contaminant transport and storage. Further study of the latter is recommended to understand the latency of legacy anthropogenic contamination of the environment., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Crown Copyright © 2020. Published by Elsevier B.V. All rights reserved.)

The atmospheric deposition of polycyclic aromatic compounds (PACs) is considered a major pathway to isolated lakes and bogs in the Athabasca oil sands region (AOSR), Canada. However, the suite of PACs measured has been limited. We report the detailed depositional history of nitrogen and sulphur heterocyclic PACs using a 210 Pb dated sediment core (1914-2015) near major developments in the AOSR. We observed (1) an exponential growth in the deposition of heterocyclic PACs to recent times with an average doubling time of 12 years, (2) significant breakpoints in PAC fluxes in the mid to late 1980s, and (3) a synchronous increase of PACs with crude oil production (r 2  = 0.82, p = 0.001). NPACs were not detected prior to the 1960s in the sediment core studied, suggesting they may hold promise in serving as indicators for atmospheric PAC deposition of industrial origin. Furthermore, a change in heterocyclic PAC distribution profiles beginning in the 1970-1980s, after the onset of mining, resembling a petcoke signature, was also observed. Significant positive correlations (p < 0.05) were observed between heterocyclic PACs, and several metal(loid)s, including priority pollutant elements, chromium and beryllium, and rare earth elements, cerium, lanthanum and yttrium (r 2  > 0.75), suggesting the potential of a common source or similar transport and fate mechanisms. Significant negative or no correlations were observed between heterocyclic PACs and other metal(loid)s, including vanadium, total mercury and lead, possibly reflecting the impact of broader regulatory controls introduced in the mid-1970s on some metal(loids) but not on PACs, including the installation of electrostatic precipitators in major upgrader stacks., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Crown Copyright © 2020. Published by Elsevier Ltd. All rights reserved.)

We evaluated anthropogenic Pb deposition along a west-east transect from the Adirondack Mountains, New York, USA (ADIR) region, the Vermont-New Hampshire-Maine, USA (VT-NH-ME) region, and Nova Scotia, Canada (NS) region using 47 210 Pb-dated lake sediment records. We used focus-corrected Pb inventories to evaluate cumulative deposition and breakpoint analysis to evaluate possible differences in timings among regions. Peak Pb concentrations decreased from west to east (ADIR region: 52-378 mg kg -1 , VT-NH-ME region: 54-253 mg kg -1 , NS: 38-140 mg kg -1 ). Cumulative deposition of anthropogenic Pb also decreased from west to east (ADIR region: 791-1344 mg m -2 , VT-NH-ME region: 209-1206 mg m -2 , NS: 52-421 mg m -2 ). The initiation of anthropogenic Pb deposition occurred progressively later along the same transect (ADIR region: 1869-1900, VT-NH-ME region: 1874-1905, NS region: 1901-1930). Previous lead isotope studies suggest that eastern Canadian Pb deposition over the past ~150 years has originated from a mix of both Canadian and U.S. sources. The results of this study indicate that anthropogenic Pb from sources west of the ADIR region were deposited in lesser amounts from west to east and/or Pb sources reflect less population density from west to east. The timing of the initiation of anthropogenic Pb deposition in the NS region suggests that Pb from gasoline may be an important source in this region., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Global atmospheric emissions and subsequent deposition of numerous metal(loid)s has increased markedly since the industrial revolution. Due to a paucity of long-term metal(loid) flux measurements, the magnitude and timing of change are largely unknown, resulting in limited ability to predict time-scales of ecosystem recovery in response to emission decreases. In the absence of long-term data, palaeo-reconstructions provide continuous records of atmospheric metal(loid) deposition on an ecosystem, and landscape, scale. Here, we use high-resolution dated lake sediment cores to reconstruct the last c. 100 years of atmospheric anthropogenic deposition of a full suite (40) of metal(loid)s near a large nickel (Ni) and copper (Cu) smelter in an other-wise largely "pristine" region of northern Canada (Thompson, Manitoba). Anthropogenic depositional fluxes were compared to other regions of Canada including Kejimkujik National Park in Nova Scotia, Experimental Lakes Area in Ontario, as well as the Flin Flon, Manitoba Cu and zinc (Zn) smelter, located ~200 km southwest of Thompson. Deposition of 12 metal(loid)s were enriched above baseline (pre-1915) levels: antimony (Sb) > palladium (Pd) > bismuth (Bi) > mercury (Hg) > cadmium (Cd) > Ni > lead (Pb) > arsenic (As) > strontium (Sr) > Cu > platinum (Pt) > Zn. Spatio-temporal patterns in depositional fluxes and inventories demonstrate that 6 of these metal(loid)s were sourced primarily from the smelter, while As, Hg, Pb, Pt, Sb and Zn were sourced primarily from global and/or regional sources. Comparison of anthropogenic fluxes and inventories to available emissions data showed that Cu and Ni deposition has plateaued since the late 1970s despite dramatic smelter emission decreases between 2005 and 2014. We hypothesize that this discrepancy is due to releases of terrestrial metal(loid)s by climate-driven permafrost degradation, which is widespread across the region and will likely continue to drive increased metal(loid) fluxes to northern Canadian lakes for unknown time-scales., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020. Published by Elsevier B.V.)

Bitumen mining and upgrading in northeastern Alberta, Canada, releases toxic pollutants into the atmosphere, including mercury (Hg) and methylmercury (MeHg). This Hg and MeHg is then deposited to the surrounding landscape; however, the fate of these contaminants remains unknown. Here, we compare snowpack chemistry to high-frequency measurements of river water quality across six watersheds (five impacted by oil sands development and one unimpacted). Catchment scale snowpack Hg and MeHg loads normalized to watershed area were highest near oil sands operations. River water Hg concentrations and loads tracked discharge and tended to be higher downstream of mining operations, while MeHg concentrations and loads increased through the summer, reflecting peak summer MeHg production rates. Except in the reference watershed, snowpack Hg and MeHg loads equaled or exceeded the amount of Hg and MeHg exported during freshet and, in some cases, the entire hydrologic year. This suggests landscapes across the oil sands region, which are dominated by low-relief wetlands and other shallow-water systems, are accumulating Hg and MeHg. Importantly, during years of high discharge, these low-relief systems appear to become better connected and flush MeHg (and Hg) from the watershed. Thus, these watersheds may act as temporary, rather than as permanent, natural repositories of oil sands contaminants.

The Athabasca Oil Sands Region (AOSR) in Alberta, Canada, is an important source of atmospheric pollutants, such as aerosols, that have repercussions on both the climate and human health. We show that the mean freezing temperature of snow-borne particles from AOSR was elevated (-7.1 ± 1.8 °C), higher than mineral dust which freezes at ∼ -15 °C and is recognized as one of the most relevant ice nuclei globally. Ice nucleation of nanosized snow samples indicated an elevated freezing ability (-11.6 ± 2.0 °C), which was statistically much higher than snow-borne particles from downtown Montreal. AOSR snow had a higher concentration (∼2 orders of magnitude) of >100 nm particles than Montreal. Triple quadrupole ICP-(QQQ)-MS/MS analysis of AOSR and Montreal snow demonstrated that most concentrations of metals, including those identified as emerging nanoparticulate contaminants, were much more elevated in AOSR in contrast to Montreal: 34.1, 34.1, 16.6, 5.8, 0.3, 0.1, and 9.4 mg/m 3 for Cr, Ni, Cu, As, Se, Cd, and Pb respectively, in AOSR and 1.3, 0.3, 2.0, <0.03, 0.1, 0.03, and 1.2 mg/m 3 in Montreal snow. High-resolution Scanning Transmission Electron Microscopy/Energy-dispersive X-ray Spectroscopy (STEM-EDS) imaging provided evidence for various anthropogenic nano-materials, including carbon nanotubes resembling structures, in AOSR snow up to 7-25 km away from major oil sands upgrading facilities. In summary, particles characterized as coming from oil sands are more efficient at ice nucleation. We discuss the potential impacts of AOSR emissions on atmospheric and microphysical processes (ice nucleation and precipitation) both locally and regionally., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Climate warming and mercury (Hg) are concurrently influencing Arctic ecosystems, altering their functioning and threatening food security. Non-anadromous Arctic char (Salvelinus alpinus) in small lakes were used to biomonitor these two anthropogenic stressors, because this iconic Arctic species is a long-lived top predator in relatively simple food webs, and yet population characteristics vary greatly, reflecting differences between lake systems. Mercury concentrations in six landlocked Arctic char populations on Cornwallis Island, Nunavut have been monitored as early as 1989, providing a novel dataset to examine differences in muscle [Hg] among char populations, temporal trends, and the relationship between climate patterns and Arctic char [Hg]. We found significant lake-to-lake differences in length-adjusted Arctic char muscle [Hg], which varied by up to 9-fold. Arctic char muscle [Hg] was significantly correlated to dissolved and particulate organic carbon concentrations in water; neither watershed area or vegetation cover explained differences. Three lakes exhibited significant temporal declines in length-adjusted [Hg] in Arctic char; the other three lakes had no significant trends. Though precipitation, temperature, wind speed, and sea ice duration were tested, no single climate variable was significantly correlated to length-adjusted [Hg] across populations. However, Arctic char Hg in Resolute Lake exhibited a significant correlation with sea ice duration, which is likely closely linked to lake ice duration, and which may impact Hg processing in lakes. Additionally, Arctic char [Hg] in Amituk Lake was significantly correlated to snow fall, which may be linked to Hg deposition. The lack of consistent temporal trends in neighboring char populations indicates that currently, within lake processes are the strongest drivers of [Hg] in char in the study lakes and potentially in other Arctic lakes, and that the influence of climate change will likely vary from lake to lake., (Crown Copyright © 2019. Published by Elsevier B.V. All rights reserved.)

Substituted diphenylamine antioxidants (SDPAs) and benzotriazole UV stabilizers (BZT-UVs) are contaminants of emerging environmental concern. However, little is known about the occurrence of these contaminants in the Arctic. In this study, we investigated the levels of 11 SDPAs and 6 BZT-UVs in livers and eggs of two seabird species, the black-legged kittiwake (Rissa tridactyla) and northern fulmar (Fulmarus glacialis), as well as the liver of ringed seals (Pusa hispida) from Canadian high- and sub-Arctic sites. The concentrations of ΣSDPAs in seabird livers (median 336 pg g -1 , wet weight (ww)) were significantly higher than the eggs (median 24 pg g -1 , ww) and the seal livers (median 38 pg g -1 , ww), suggesting liver was a primary tissue of SDPA accumulation in seabirds and that seabirds were at greater risk of exposure to SDPAs than marine mammals in the Arctic. The predominant SDPA was monostyryl octyl-diphenylamine and this compound was detected in every seabird and seal sample, indicating the widespread distribution of this contaminant in Arctic food webs. Unlike SDPAs, the detection rate and concentrations of BZT-UVs in seals were higher than in seabirds. The compound 2-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol (UV329) or its isomer 2-(2H-benzotriazol-2-yl)-4-(tert-butyl)-6-(sec-butyl) phenol (UV350) was the predominant BZT-UVs in seals, with the concentrations of ΣBZT-UVs between 4  pg g -1 (ww) (median: 2.36 × 10 3  pg g -1 , ww). This is the first report of the different distribution patterns of SDPAs and BZT-UVs in wildlife from Canadian Arctic sites., (Crown Copyright © 2019. Published by Elsevier B.V. All rights reserved.)

Polycyclic aromatic compounds (PACs) can have multiple sources in the Athabasca Oil Sands Region (AOSR). The current study was designed to identify and explore the potential of nitrogen heterocyclic PACs (NPACs) as source indicators in snowpack, lake sediment and passive air samples from the AOSR during 2014-2015. Source samples including petroleum coke (petcoke), haul road dust, and unprocessed oil sands were also analyzed. Samples were analyzed using comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry, and liquid chromatography-high resolution Orbitrap mass spectrometry. Over 200 NPACs were identified and classified into at least 24 isomer groups, including alkylated carbazoles, benzocarbazoles, and indenoquinolines. Levels of NPACs in environmental samples decreased with distance from the main developments and with increasing depth in lake sediments but were detected within 50 km from the major developments. The composition profiles of several NPAC isomer classes, such as dimethylcarbazoles, showed that petcoke had a distinct distribution of NPACs compared to the haul road dust and unprocessed oil sands ores and was the most similar source material to near-field environmental samples. These results suggest that petcoke is a major contributing source for the identified NPACs and that these compounds have the potential to be used as source indicators for future research in the AOSR.

Methylmercury (MeHg) is a central nervous system toxicant and exposures can adversely affect the health of marine mammals. Mercuric selenide (HgSe) in marine mammal tissues is hypothesized to result from a protective detoxification mechanism, but toxicokinetic processes contributing to its formation are poorly understood. Here, new data is reported on speciated Hg concentrations in multiple organs of n = 56 ringed seals (Phoca hispida) from Labrador, Canada, and compare concentrations to previously published data from Greenland seals. A higher proportion of Hg is found to accumulate in the kidney of young-of-the-year (YOY) ringed seals compared to adults. A toxicokinetic model for Hg species is developed and evaluated to better understand factors affecting variability in Hg concentrations among organs and across life stages. Prior work postulated that HgSe formation only occurs in the liver of mature seals, but model results suggest HgSe formation occurs across all life stages. Higher proportions of HgSe in mature seal livers compared to YOY seals likely results from the slow accumulation and elimination of HgSe (total body half-life = 500 days) compared to other Hg species. HgSe formation in the liver reduces modeled blood concentrations of MeHg by only 6%. Thus, HgSe formation may not substantially reduce MeHg transport across the blood-brain barrier of ringed seals, leaving them susceptible to the neurotoxic effects of MeHg exposure., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Tailings ponds created during industrial bitumen extraction from the Athabasca Oil Sands Region (AOSR), Alberta, Canada, have been shown to contain numerous contaminants, such as polycyclic aromatic compounds and naphthenic acids, and to slowly leak into adjacent ground and surface waters. Despite elevated concentrations of total mercury (THg) in nearby Athabasca River waters downstream of the AOSR developments, to date there are no published studies of THg or methylmercury (MeHg; a potent neurotoxin) in the AOSR tailings ponds. Here we present concentrations of THg and MeHg, as well as various water chemistry parameters, within four AOSR tailings ponds. Concentrations of SO 4 2- , Na, and Cl were elevated in tailings ponds relative to nearby freshwaters. Surface water concentrations of THg (filtered: 0.15-0.57 ng/L) and MeHg (unfiltered: <0.02-0.53 ng/L; filtered: <0.02-0.32 ng/L), though, were generally low in the tailings ponds, with the highest concentrations observed in the oldest pond. In the mature fine tailings that settle out in the ponds, concentrations of THg (37.0-197 ng/g) and MeHg (0.10-0.52 ng/g) were also low, with the highest concentrations again in the oldest pond. We calculated that if all the dissolved THg and MeHg potentially leaking annually from the tailings ponds entered the nearby Athabasca River, river THg and MeHg concentrations would increase by only 0.01% and 0.03%, respectively. Overall, these ponds are likely not significant sources of THg or MeHg to nearby ground and surface waters, although due to the potential for Hg methylation to occur in the ponds themselves, other tailings ponds in the AOSR should be monitored to ensure that concentrations of MeHg in them are also low.3 , Na, and Cl were elevated in tailings ponds relative to nearby freshwaters. Surface water concentrations of THg (filtered: 0.15-0.57 ng/L) and MeHg (unfiltered: <0.02-0.53 ng/L; filtered: <0.02-0.32 ng/L), though, were generally low in the tailings ponds, with the highest concentrations observed in the oldest pond. In the mature fine tailings that settle out in the ponds, concentrations of THg (37.0-197 ng/g) and MeHg (0.10-0.52 ng/g) were also low, with the highest concentrations again in the oldest pond. We calculated that if all the dissolved THg and MeHg potentially leaking annually from the tailings ponds entered the nearby Athabasca River, river THg and MeHg concentrations would increase by only 0.01% and 0.03%, respectively. Overall, these ponds are likely not significant sources of THg or MeHg to nearby ground and surface waters, although due to the potential for Hg methylation to occur in the ponds themselves, other tailings ponds in the AOSR should be monitored to ensure that concentrations of MeHg in them are also low., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Mercury is a global pollutant released into the biosphere by varied human activities including coal combustion, mining, artisanal gold mining, cement production, and chemical production. Once released to air, land and water, the addition of carbon atoms to mercury by bacteria results in the production of methylmercury, the toxic form that bioaccumulates in aquatic and terrestrial food chains resulting in elevated exposure to humans and wildlife. Global recognition of the mercury contamination problem has resulted in the Minamata Convention on Mercury, which came into force in 2017. The treaty aims to protect human health and the environment from human-generated releases of mercury curtailing its movement and transformations in the biosphere. Coincident with the treaty's coming into force, the 13th International Conference of Mercury as a Global Pollutant (ICMGP-13) was held in Providence, Rhode Island USA. At ICMGP-13, cutting edge research was summarized and presented to address questions relating to global and regional sources and cycling of mercury, how that mercury is methylated, the effects of mercury exposure on humans and wildlife, and the science needed for successful implementation of the Minamata Convention. Human activities have the potential to enhance mercury methylation by remobilizing previously released mercury, and increasing methylation efficiency. This synthesis concluded that many of the most important factors influencing the fate and effects of mercury and its more toxic form, methylmercury, stem from environmental changes that are much broader in scope than mercury releases alone. Alterations of mercury cycling, methylmercury bioavailability and trophic transfer due to climate and land use changes remain critical uncertainties in effective implementation of the Minamata Convention. In the face of these uncertainties, important policy and management actions are needed over the short-term to support the control of mercury releases to land, water and air. These include adequate monitoring and communication on risk from exposure to various forms of inorganic mercury as well as methylmercury from fish and rice consumption. Successful management of global and local mercury pollution will require integration of mercury research and policy in a changing world.

High tech applications, primarily photovoltaics, have greatly increased demand for the rare and versatile but toxic element tellurium (Te). Here we examine dated lake sediment Te concentration profiles collected near potential point sources (metal smelters, coal mining/combustion facilities, oil sands operations) and from rural regions and remote natural areas of Canada. Te contamination was most prevalent near a Cu/Zn smelter where observed deposition infers 21 g Te released per metric ton (t) of Cu processed. Globally, 9,500 t is predicted to have been atmospherically deposited near Cu smelters post-1900. In a remote area of central Canada (Experimental Lakes Area; ELA), preindustrial Te deposition rates were equivalent to the estimated average global mass flux supplied from natural sources; however more surprisingly, modern Te deposition rates were 6-fold higher and comparable with Te measurements in precipitation. We therefore suggest that sediment cores reliably record atmospheric Te deposition and that anthropogenic activities have significantly augmented atmospheric Te levels, making it an emerging contaminant of potential concern. Lake water residence time was found to influence lake sediment Te inventories among lakes within a region. The apparent settling rate for Te was comparable to macronutrients (C, N, P), likely indicative of significant biological processing of Te.

We review recent progress in our understanding of the global cycling of mercury (Hg), including best estimates of Hg concentrations and pool sizes in major environmental compartments and exchange processes within and between these reservoirs. Recent advances include the availability of new global datasets covering areas of the world where environmental Hg data were previously lacking; integration of these data into global and regional models is continually improving estimates of global Hg cycling. New analytical techniques, such as Hg stable isotope characterization, provide novel constraints of sources and transformation processes. The major global Hg reservoirs that are, and continue to be, affected by anthropogenic activities include the atmosphere (4.4-5.3 Gt), terrestrial environments (particularly soils: 250-1000 Gg), and aquatic ecosystems (e.g., oceans: 270-450 Gg). Declines in anthropogenic Hg emissions between 1990 and 2010 have led to declines in atmospheric Hg 0 concentrations and Hg II wet deposition in Europe and the US (- 1.5 to - 2.2% per year). Smaller atmospheric Hg 0 declines (- 0.2% per year) have been reported in high northern latitudes, but not in the southern hemisphere, while increasing atmospheric Hg loads are still reported in East Asia. New observations and updated models now suggest high concentrations of oxidized Hg II in the tropical and subtropical free troposphere where deep convection can scavenge these Hg II reservoirs. As a result, up to 50% of total global wet Hg II deposition has been predicted to occur to tropical oceans. Ocean Hg 0 evasion is a large source of present-day atmospheric Hg (approximately 2900 Mg/year; range 1900-4200 Mg/year). Enhanced seawater Hg 0 levels suggest enhanced Hg 0 ocean evasion in the intertropical convergence zone, which may be linked to high Hg II deposition. Estimates of gaseous Hg 0 emissions to the atmosphere over land, long considered a critical Hg source, have been revised downward, and most terrestrial environments now are considered net sinks of atmospheric Hg due to substantial Hg uptake by plants. Litterfall deposition by plants is now estimated at 1020-1230 Mg/year globally. Stable isotope analysis and direct flux measurements provide evidence that in many ecosystems Hg 0 deposition via plant inputs dominates, accounting for 57-94% of Hg in soils. Of global aquatic Hg releases, around 50% are estimated to occur in China and India, where Hg drains into the West Pacific and North Indian Oceans. A first inventory of global freshwater Hg suggests that inland freshwater Hg releases may be dominated by artisanal and small-scale gold mining (ASGM; approximately 880 Mg/year), industrial and wastewater releases (220 Mg/year), and terrestrial mobilization (170-300 Mg/year). For pelagic ocean regions, the dominant source of Hg is atmospheric deposition; an exception is the Arctic Ocean, where riverine and coastal erosion is likely the dominant source. Ocean water Hg concentrations in the North Atlantic appear to have declined during the last several decades but have increased since the mid-1980s in the Pacific due to enhanced atmospheric deposition from the Asian continent. Finally, we provide examples of ongoing and anticipated changes in Hg cycling due to emission, climate, and land use changes. It is anticipated that future emissions changes will be strongly dependent on ASGM, as well as energy use scenarios and technology requirements implemented under the Minamata Convention. We predict that land use and climate change impacts on Hg cycling will be large and inherently linked to changes in ecosystem function and global atmospheric and ocean circulations. Our ability to predict multiple and simultaneous changes in future Hg global cycling and human exposure is rapidly developing but requires further enhancement.

Snowpacks in the Alberta Oil Sands Region (AOSR) of Canada contain elevated loadings of methylmercury (MeHg; a neurotoxin that biomagnifies through foodwebs) due to oil sands related activities. At sites ranging from 0 to 134 km from the major AOSR upgrading facilities, we examined sources of MeHg by quantifying potential rates of MeHg production in snowpacks and melted snow using mercury stable isotope tracer experiments, as well as quantifying concentrations of MeHg on particles in snowpacks (pMeHg). At four sites, methylation rate constants were low in snowpacks (k m = 0.001-0.004 d -1 ) and nondetectable in melted snow, except at one site (k m = 0.0007 d -1 ). The ratio of methylation to demethylation varied between 0.3 and 1.5, suggesting that the two processes are in balance and that in situ production is unlikely an important net source of MeHg to AOSR snowpacks. pMeHg concentrations increased linearly with distance from the upgraders (R 2 = 0.71, p < 0.0001); however, snowpack total particle and pMeHg loadings decreased exponentially over this same distance (R 2 = 0.49, p = 0.0002; R 2 = 0.56, p < 0.0001). Thus, at near-field sites, total MeHg loadings in snowpacks were high due to high particle loadings, even though particles originating from industrial activities were not MeHg rich compared to those at remote sites. More research is required to identify the industrial sources of snowpack particles in the AOSR.

We examined the historical deposition of polycyclic aromatic compounds (PACs) recorded in radiometrically-dated lake sediment cores from a small, conventional oil and gas operation in the southern Northwest Territories (Cameron Hills), and placed these results in the context of previously published work from three other important regions of western Canada: (1) the Athabasca oil sands region in Alberta; (2) Cold Lake, Alberta; and (3) the Mackenzie Delta, NT. Sediment PAC records from the Cameron Hills showed no clear changes in either source or concentrations coincident with the timing of development in these regions. Changes were small in comparison to the clear increases in both parent and alkyl-substituted PACs in response to industrial development from the Athabasca region surface mining of oil sands, where parent PAC diagnostic ratios indicated a shift from pyrogenic sources (primarily wood and coal burning) in pre-development sediments to more petrogenically-sourced PACs in modern sediments. Cores near in-situ oil sand extraction operations showed only modest increases in PAC deposition. This work directly compares the history and trajectory of contamination in lake ecosystems in areas of western Canada impacted by the most common types of hydrocarbon extraction activities, and provides a context for assessing the environmental impacts of oil and gas development in the future., (Crown Copyright © 2017. Published by Elsevier Ltd. All rights reserved.)

High-resolution records of anthropogenic mercury (Hg) deposition were constructed from 9 lakes located 5-75km from the Flin Flon, Manitoba smelter (formerly one of North America's largest atmospheric Hg point sources) and 5 lakes in Experimental Lakes Area (ELA), Ontario; a region remote from major Hg point sources. Anthropogenic Hg deposition, as both a flux and inventory, was determined after accounting for lake-specific natural Hg background concentrations, changes in sedimentation and sediment focusing. Results show that records of anthropogenic flux and inventory of Hg were remarkably consistent among the ELA lakes, but varied by 2 orders of magnitude among Flin Flon lakes. The relation between Hg inventories (normalized for prevailing wind direction) and distance from the smelter was used to estimate the total Hg fallout within a 50km radius in 5year time-steps, thus providing a quantitative spatial-temporal Hg depositional history for the Flin Flon region. The same relation solved for 8 cardinal directions weighted by the inverse of the previously applied wind direction normalization generates a map of Hg inventory and deposition on the landscape (Supplementary video). This novel application of sediment core data constructs a landscape model and allows for a visualization of contaminant deposition with respect to a point major source in both space and time. The propensity for Hg to undergo long-range, even global transport explains why Hg deposition within 50km of Flin Flon was ~11% of estimated releases. That is until smelter releases were reduced >10-fold (post-2000), after which observed deposition exceeded smelter releases, suggesting landscape re-emission/remobilization of legacy Hg is a major ongoing regional source of Hg., (Crown Copyright © 2017. Published by Elsevier B.V. All rights reserved.)

Freshwaters in the Athabasca Oil Sands Region (AOSR) are vulnerable to the atmospheric emissions and land disturbances caused by the local oil sands industry; however, they are also affected by climate change. Recent observations of increases in aquatic primary production near the main development area have prompted questions about the principal drivers of these limnological changes. Is the enhanced primary production due to deposition of nutrients (nitrogen and phosphorus) from local industry or from recent climatic changes? Here, we use downcore, spectrally-inferred chlorophyll-a (VRS-chla) profiles (including diagenetic products) from 23 limnologically-diverse lakes with undisturbed catchments to characterize the pattern of primary production increases in the AOSR. Our aim is to better understand the relative roles of the local oil sands industry versus climate change in driving aquatic primary production trends. Nutrient deposition maps, generated using geostatistical interpolations of spring-time snowpack measurements from a grid pattern across the AOSR, demonstrate patterns of elevated total phosphorus, total nitrogen, and bioavailable nitrogen deposition around the main area of industrial activity. However, this pattern is not observed for bioavailable phosphorus. Our paleolimnological findings demonstrate consistently greater VRS-chla concentrations compared to pre-oil sands development levels, regardless of morphological and limnological characteristics, landscape position, bioavailable nutrient deposition, and dibenzothiophene (DBT)-inferred industrial impacts. Furthermore, breakpoint analyses on VRS-chla concentrations across a gradient of DBT-inferred industrial impact show limited evidence of a contemporaneous change among lakes. Despite the contribution of bioavailable nitrogen to the landscape from industrial activities, we find no consistency in the spatial pattern and timing of VRS-chla shifts with an industrial fertilizing signal. Instead, significant positive correlations were observed between VRS-chla and annual and seasonal temperatures. Our findings suggest warmer air temperatures and likely decreased ice covers are important drivers of enhanced aquatic primary production across the AOSR.

In temperate regions of Canada, mercury (Hg) concentrations in biota and the magnitude of Hg biomagnification through food webs vary between neighboring lakes and are related to water chemistry variables and physical lake features. However, few studies have examined factors affecting the variable Hg concentrations in landlocked Arctic char (Salvelinus alpinus) or the biomagnification of Hg through their food webs. We estimated the food web structure of six high Arctic lakes near Resolute Bay, Nunavut, Canada, using stable carbon (δ(13)C) and nitrogen (δ(15)N) isotopes and measured Hg (total Hg (THg) in char, the only fish species, and methylmercury (MeHg) in chironomids and zooplankton) concentrations in biota collected in 2010 and 2011. Across lakes, δ(13)C showed that benthic carbon (chironomids) was the dominant food source for char. Regression models of log Hg versus δ(15)N (of char and benthic invertebrates) showed positive and significant slopes, indicting Hg biomagnification in all lakes, and higher slopes in some lakes than others. However, no principal components (PC) generated using all water chemistry data and physical characteristics of the lakes predicted the different slopes. The PC dominated by aqueous ions was a negative predictor of MeHg concentrations in chironomids, suggesting that water chemistry affects Hg bioavailability and MeHg concentrations in these lower-trophic-level organisms. Furthermore, regression intercepts were predicted by the PCs dominated by catchment area, aqueous ions, and MeHg. Weaker relationships were also found between THg in small char or MeHg in pelagic invertebrates and the PCs dominated by catchment area, and aqueous nitrate and MeHg. Results from these high Arctic lakes suggest that Hg biomagnification differs between systems and that their physical and chemical characteristics affect Hg concentrations in lower-trophic-level biota., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Atmospheric deposition of metals originating from a variety of sources, including bitumen upgrading facilities and blowing dusts from landscape disturbances, is of concern in the Athabasca oil sands region of northern Alberta, Canada. Mercury (Hg) is of particular interest as methylmercury (MeHg), a neurotoxin which bioaccumulates through foodwebs, can reach levels in fish and wildlife that may pose health risks to human consumers. We used spring-time sampling of the accumulated snowpack at sites located varying distances from the major developments to estimate winter 2012 Hg loadings to a ∼20 000 km(2) area of the Athabasca oil sands region. Total Hg (THg; all forms of Hg in a sample) loads were predominantly particulate-bound (79 ± 12%) and increased with proximity to major developments, reaching up to 1000 ng m(-2). MeHg loads increased in a similar fashion, reaching up to 19 ng m(-2) and suggesting that oil sands developments are a direct source of MeHg to local landscapes and water bodies. Deposition maps, created by interpolation of measured Hg loads using geostatistical software, demonstrated that deposition resembled a bullseye pattern on the landscape, with areas of maximum THg and MeHg loadings located primarily between the Muskeg and Steepbank rivers. Snowpack concentrations of THg and MeHg were significantly correlated (r = 0.45-0.88, p < 0.01) with numerous parameters, including total suspended solids (TSS), metals known to be emitted in high quantities from the upgraders (vanadium, nickel, and zinc), and crustal elements (aluminum, iron, and lanthanum), which were also elevated in this region. Our results suggest that at snowmelt, a complex mixture of chemicals enters aquatic ecosystems that could impact biological communities of the oil sands region.

The absence of well-executed environmental monitoring in the Athabasca oil sands (Alberta, Canada) has necessitated the use of indirect approaches to determine background conditions of freshwater ecosystems before development of one of the Earth's largest energy deposits. Here, we use highly resolved lake sediment records to provide ecological context to ∼50 y of oil sands development and other environmental changes affecting lake ecosystems in the region. We show that polycyclic aromatic hydrocarbons (PAHs) within lake sediments, particularly C1-C4-alkylated PAHs, increased significantly after development of the bitumen resource began, followed by significant increases in dibenzothiophenes. Total PAH fluxes in the modern sediments of our six study lakes, including one site ∼90 km northwest of the major development area, are now ∼2.5-23 times greater than ∼1960 levels. PAH ratios indicate temporal shifts from primarily wood combustion to petrogenic sources that coincide with greater oil sands development. Canadian interim sediment quality guidelines for PAHs have been exceeded since the mid-1980s at the most impacted site. A paleoecological assessment of Daphnia shows that this sentinel zooplankter has not yet been negatively impacted by decades of high atmospheric PAH deposition. Rather, coincident with increases in PAHs, climate-induced shifts in aquatic primary production related to warmer and drier conditions are the primary environmental drivers producing marked daphniid shifts after ∼1960 to 1970. Because of the striking increase in PAHs, elevated primary production, and zooplankton changes, these oil sands lake ecosystems have entered new ecological states completely distinct from those of previous centuries.

Mercury (Hg) contamination in aquatic systems remains a global concern because the organic form, methyl Hg (MeHg), can biomagnify to harmful concentrations in fish, fish-eating wildlife, and humans. Food web transfer of MeHg has been explored using models of log MeHg versus relative trophic position (nitrogen isotopes, δ(15)N), but regression slopes vary across systems for unknown reasons. In this study, MeHg biomagnification was determined for 11 lake food webs in Kejimkujik National Park, Nova Scotia, Canada, and compared to physical and chemical lake characteristics using principal component and multiple regression analyses. MeHg biomagnification (regression slopes of log MeHg versus baseline-adjusted δ(15)N for fishes and invertebrates) varied significantly across lakes and was higher in systems with lower aqueous nutrient/MeHg/chloride scores. This is one of the largest, consistent data sets available on MeHg biomagnification through temperate lake food webs and the first study to use a principal component and multiple regression approach to understand how lake chemical and physical characteristics interact to affect biomagnification among systems. Overall, our results show that the magnitude of MeHg biomagnification through lake food webs is related to the chemical and physical characteristics of the systems, but the underlying mechanisms warrant further investigation.

Mercury in the Arctic is an important environmental and human health issue. The reliance of Northern Peoples on traditional foods, such as marine mammals, for subsistence means that they are particularly at risk from mercury exposure. The cycling of mercury in Arctic marine systems is reviewed here, with emphasis placed on the key sources, pathways and processes which regulate mercury levels in marine food webs and ultimately the exposure of human populations to this contaminant. While many knowledge gaps exist limiting our ability to make strong conclusions, it appears that the long-range transport of mercury from Asian emissions is an important source of atmospheric Hg to the Arctic and that mercury methylation resulting in monomethylmercury production (an organic form of mercury which is both toxic and bioaccumulated) in Arctic marine waters is the principal source of mercury incorporated into food webs. Mercury concentrations in biological organisms have increased since the onset of the industrial age and are controlled by a combination of abiotic factors (e.g., monomethylmercury supply), food web dynamics and structure, and animal behavior (e.g., habitat selection and feeding behavior). Finally, although some Northern Peoples have high mercury concentrations of mercury in their blood and hair, harvesting and consuming traditional foods have many nutritional, social, cultural and physical health benefits which must be considered in risk management and communication., (Copyright © 2012 Elsevier Inc. All rights reserved.)

Methylmercury (MeHg) is a potent neurotoxin that has been demonstrated to biomagnify in Arctic freshwater foodwebs to levels that may be of concern to Inuit peoples subsisting on freshwater fish, for example. The key process initiating the bioaccumulation and biomagnification of MeHg in foodwebs is the methylation of inorganic Hg(II) to form MeHg, and ultimately how much MeHg enters foodwebs is controlled by the production and availability of MeHg in a particular water body. We used isotopically enriched Hg stable isotope tracers in sediment core incubations to measure potential rates of Hg(II) methylation and investigate the controls on MeHg production in High Arctic wetland ponds in the Lake Hazen region of northern Ellesmere Island (Nunavut, Canada). We show here that MeHg concentrations in sediments are primarily controlled by the sediment methylation potential and the quantity of Hg(II) available for methylation, but not by sediment demethylation potential. Furthermore, MeHg concentrations in pond waters are controlled by MeHg production in sediments, overall anaerobic microbial activity, and photodemethylation in the water column.

The sources of methylmercury (MeHg; the toxic form of mercury that is biomagnified through foodwebs) to Arctic freshwater organisms have not been clearly identified. We used a mass balance approach to quantify MeHg production in two wetland ponds in the Lake Hazen region of northern Ellesmere Island, NU, in the Canadian High Arctic and to evaluate the importance of these systems as sources of MeHg to Arctic foodwebs. We show that internal production (1.8-40 ng MeHg m(-2) d(-1)) is a much larger source of MeHg than external inputs from direct atmospheric deposition (0.029-0.051 ng MeHg m(-2) d(-1)), as expected. Furthermore, MeHg cycling in these systems is dominated by Hg(II) methylation and MeHg photodemethylation (2.0-33 ng MeHg m(-2) d(-1)), which is a sink for a large proportion of the MeHg produced by Hg(II) methylation in these ponds. We also show that MeHg production in the two study ponds is comparable to what has previously been measured in numerous more southerly systems known to be important MeHg sources, such as temperate wetlands and lakes, demonstrating that wetland ponds in the High Arctic are important sources of MeHg to local aquatic foodwebs.

Polar bears (Ursus maritimus) are being impacted by climate change and increased exposure to pollutants throughout their northern circumpolar range. In this study, we quantified concentrations of total mercury (THg) in the hair of polar bears from Canadian high- (southern Beaufort Sea, SBS) and sub- (western Hudson Bay, WHB) Arctic populations. Concentrations of THg in polar bears from the SBS population (14.8 ± 6.6 μg g(-1)) were significantly higher than in polar bears from WHB (4.1 ± 1.0 μg g(-1)). On the basis of δ(15)N signatures in hair, in conjunction with published δ(15)N signatures in particulate organic matter and sediments, we estimated that the pelagic and benthic food webs in the SBS are ∼ 4.7 and ∼ 4.0 trophic levels long, whereas in WHB they are only ∼ 3.6 and ∼ 3.3 trophic levels long. Furthermore, the more depleted δ(13)C ratios in hair from SBS polar bears relative to those from WHB suggests that SBS polar bears feed on food webs that are relatively more pelagic (and longer), whereas polar bears from WHB feed on those that are relatively more benthic (and shorter). Food web length and structure accounted for ∼ 67% of the variation we found in THg concentrations among all polar bears across both populations. The regional difference in polar bear hair THg concentrations was also likely due to regional differences in water-column concentrations of methyl Hg (the toxic form of Hg that biomagnifies through food webs) available for bioaccumulation at the base of the food webs. For example, concentrations of methylated Hg at mid-depths in the marine water column of the northern Canadian Arctic Archipelago were 79.8 ± 37.3 pg L(-1), whereas, in HB, they averaged only 38.3 ± 16.6 pg L(-1). We conclude that a longer food web and higher pelagic concentrations of methylated Hg available to initiate bioaccumulation in the BS resulted in higher concentrations of THg in polar bears from the SBS region compared to those inhabiting the western coast of HB.

Mercury (Hg) profiles were compared to profiles of climate indicators including microfossil remains and algal-derived or S2 carbon (C) in dated sediment cores from 14 lakes spanning latitudinal and longitudinal gradients across the Canadian high and subarctic. Hg fluxes increased postindustrialization (post-∼1850) in 11 of these lakes (postindustrialization Hg fluxes (ΔHgF(F)) = 2-24 μg m(-2) y(-1)). Correction of HgF(F) for catchment contributions demonstrated that Hg deposition originating from catchment-independent factors, such as atmospheric deposition, increased since industrialization in all 14 lakes. Several of these lakes also showed postindustrial shifts in algal assemblages consistent with climate-induced changes. Eleven lakes showed post-1850s increases in S2F(F), suggesting that lake primary productivity has recently increased in the majority of our sites (ΔS2F(F) = 0.1-4 g m(-2) y(-1)). Other studies have interpreted significant relationships between Hg:S2 concentrations in Arctic sediment as support for the algal scavenging hypothesis, which postulates that Hg fluxes to Arctic sediments are largely driven by S2. However, in six of our lakes we observed no Hg:S2 relationship, and in one lake a significant negative Hg:S2 relationship was observed due to increased Hg and decreased S2 C deposition during the postindustrialization period. In six of the seven lakes where a significant positive Hg:S2 relationship was observed, algal assemblages either did not change through time or the timing of the shifts did not correspond to changes in Hg deposition. Our results demonstrate that, although Arctic lakes are experiencing a myriad of changes, including increased Hg and S2 deposition or changing algal assemblages, increased lake primary productivity does not appear to be driving changes in Hg fluxes to sediments.

From 2003 to 2007, concentrations of total mercury and methylmercury (THg and MeHg) were continuously measured in two Canadian sub-Arctic rivers (the Nelson and the Churchill) that drain into western Hudson Bay. THg and MeHg concentrations were low in the Nelson River (mean i standard deviation, 0.88 +/- 0.33 and 0.05 +/- 0.03 ng L(-1), respectively). The Churchill River, however, had high concentrations of Hg, particularly MeHg (1.96 +/- 0.8 and 0.18 +/- 0.09 ng L(-1), respectively) and hence may be an important source of MeHg to organisms feeding in the Churchill River estuary. A large portion of THg in the Nelson River was particulate-bound (39 +/- 23%), while in the Churchill River, most was in the dissolved form (78 +/- 15%) and is likely dissolved organic carbon (DC)-bound Hg originating in the surrounding wetlands. In fact, both the Nelson and Churchill Rivers had high DOC concentrations and were therefore large exporters of DOC to Hudson Bay (1480 +/- 723 and 392 +/- 309 x 10(3) t year(-1), respectively) compared to rivers to the south and east Despite high Churchill River Hg concentrations, due to large Nelson River flows, average THg and MeHg exports to Hudson Bay from the Churchill River (37 +/- 28 and 4 +/- 4 kg year(-1), respectively) were about one-third and half the Nelson River exports (113 +/- 52 and 9 +/- 4 kg year(-1)). Interestingly, combined Hg exports to Hudson Bay from Nelson and Churchill River discharge are comparable to THg inputs from Hudson Bay springtime snowmelt (177 +/-140 kg year(-1)) but are approximately 13 times greater than MeHg snowmelt inputs (1 +/- 1 kg year(-1)). Although Hg inputs from rivers and snowmelt together may account for a large portion of the THg pool in Hudson Bay, these inputs account for a lesser portion of the MeHg pool, thus highlighting the importance of water column Hg(ll) methylation as a source of MeHg to Hudson Bay marine food webs.

Distribution of total mercury (THg), gaseous elemental Hg(0) (GEM), monomethyl Hg (MMHg), and dimethyl Hg (DMHg) was examined in marine waters of the Canadian Arctic Archipelago (CAA), Hudson Strait, and Hudson Bay. Concentrations of THg were low throughout the water column in all regions sampled (mean +/- standard deviation; 0.40 +/- 0.47 ng L(-1)). Concentrations of MMHg were also generally low atthe surface (23.8 +/- 9.9 pg L(-1)); however at mid- and bottom depths, MMHg was present at concentrations sufficient to initiate bioaccumulation of MMHg through Arctic marine foodwebs (maximum 178 pg L(-1); 70.3 +/- 37.3 pg L(-1)). In addition, at mid- and bottom depths, the % of THg that was MMHg was high (maximum 66%; 28 +/- 16%), suggesting that active methylation of inorganic Hg(II) occurs in deep Arctic marine waters. Interestingly, there was a constant, near 1:1, ratio between concentrations of MMHg and DMHg at all sites and depths, suggesting that methylated Hg species are in equilibrium with each other and/or are produced by similar processes throughout the water column. Our results also demonstrate that oceanographic processes, such as water regeneration and vertical mixing, affect Hg distribution in marine waters. Vertical mixing, for example, likely transported MMHg and DMHg upward from production zones at some sites, resulting in elevated concentrations of these species in surface waters (up to 68.0 pg L(-1)) where primary production and thus uptake of MMHg by biota is potentially highest. Finally, calculated instantaneous ocean-atmosphere fluxes of gaseous Hg species demonstrated that Arctic marine waters are a substantial source of DMHg and GEM to the atmosphere (27.3 +/- 47.8 and 130 +/- 138 ng m(-2) day(-1), respectively) during the ice-free season.

We sampled seawater and snowpacks in the Canadian high Arctic for methylated species of mercury (Hg). We discovered that, although seawater sampled under the sea ice had very low concentrations of total Hg (THg, all forms of Hg in a sample; on average 0.14-0.24 ng L(-1)), 30-45% of the THg was in the monomethyl Hg (MMHg) form (on average 0.057-0.095 ng L(-1)), making seawater itself a direct source of MMHg for biomagnification through marine food webs. Seawater under the ice also contained high concentrations of gaseous elemental Hg (GEM; 129 +/- 36 pg L(-1)), suggesting that open water regions such as polynyas and ice leads were a net source of approximately 130 +/- 30 ng Hg m(-2) day(-1) to the atmosphere. We also found 11.1 +/- 4.1 pg L(-1) of dimethyl Hg (DMHg) in seawater and calculated that there could be a significant flux of DMHg to the atmosphere from open water regions. This flux could then resultin MMHg deposition into nearby snowpacks via oxidation of DMHg to MMHg in the atmosphere. In fact, we found high concentrations of MMHg in a few snowpacks near regions of open water. Interestingly, we discovered a significant log-log relationship between Cl- concentrations in snowpacks and concentrations of THg. We hypothesize that as Cl- concentrations in snowpacks increase, inorganic Hg(II) occurs principally as less reducible chloro complexes and, hence, remains in an oxidized state. As a result, snowpacks that receive both marine aerosol deposition of Cl- and deposition of Hg(II) via springtime atmospheric Hg depletion events, for example, may contain significant loads of Hg(II). Overall, though, the median wet/dry loads of Hg in the snowpacks we sampled in the high Arctic (5.2 mg THg ha(-1) and 0.03 mg MMHg ha(-1)) were far below wet-only annual THg loadings throughout southern Canada and most of the U.S. (22-200 mg ha(-1)). Therefore, most Arctic snowpacks contribute

Mercury (Hg) in some Arctic marine mammals has increased to levels that may be toxic to Northern peoples consuming them as traditional food. It has been suggested that sunlight-induced atmospheric reactions called springtime atmospheric Hg depletion events (AMDEs) result in the loading of -150-300 tons of Hg to the Canadian Arctic archipelago each spring and that AMDEs are the ultimate source of Hg to Arctic foodwebs. AMDEs result from the oxidation of gaseous elemental Hg0 (GEM) in Arctic atmospheres to reactive gaseous Hg (RGM) and particulate Hg (pHg), both of which fall out of the atmosphere to snowpacks. We studied the springtime cycling of Hg between air and snowpacks near Churchill, Manitoba, for 2 years to determine the net input of Hg to Hudson Bay from AMDEs. In 2004, we monitored atmospheric concentrations of GEM, pHg, and RGM while simultaneously measuring concentrations of total Hg (THg) in surface snow collected over the sea ice on Hudson Bay. During numerous springtime AMDEs, concentrations of THg in surface snow increased, often to over 60 ng/L, demonstrating that AMDEs resulted in deposition of oxidized Hg (Hg(II)) to snowpacks. However, immediatelyfollowing AMDEs, average concentrations of THg in snow declined drastically from between 67.8+/-7.7 ng/L during AMDEs to only 4.25+/-1.85 ng/L four or more days following them. In 2003, we measured THg in surface snow collected daily over the sea ice and total gaseous Hg (TGM) concentrations in the interstitial airspaces of snowpacks. When concentrations of THg in the surface snow decreased, concentrations of TGM in interstitial airspaces of the snowpack increased sharply from between approximately 1.4-3.4 ng/m(3) to between approximately 20-150 ng/m(3), suggesting thatthere was a reduction of deposited Hg(II) to GEM, which then diffused out of snowpacks. At snowmelt in both 2003 and 2004, average concentrations of THg in meltwater collected over Hudson Bay were only 4.04+/-2.01 ng/L. Using concentrations of THg in meltwater and snow water equivalent, we estimated a net springtime loading of only 2.1+/-1.7 mg/ha of Hg to Hudson Bay from AMDEs, indicating that only a small portion of the Hg(II) deposited during AMDEs enters Hudosn Bay each spring.

We identified some of the sources and sinks of monomethyl mercury (MMHg) and inorganic mercury (HgII) on Ellesmere Island in the Canadian High Arctic. Atmospheric Hg depletion events resulted in the deposition of Hg(II) into the upper layers of snowpacks, where concentrations of total Hg (all forms of Hg) reached over 20 ng/L. However, our data suggest that much of this deposited Hg(II) was rapidly photoreduced to Hg(0) which then evaded back to the atmosphere. As a result, we estimate that net wet and dry deposition of Hg(II) during winter was lower at our sites (0.4-5.9 mg/ha) than wet deposition in more southerly locations in Canada and the United States. We also found quite high concentrations of monomethyl Hg (MMHg) in snowpacks (up to 0.28 ng/L), and at times, most of the Hg in snowpacks was present as MMHg. On the Prince of Wales Icefield nearthe North Water Polynya, we observed a significant correlation between concentrations of Cl and MMHg in snow deposited in the spring, suggesting a marine source of MMHg. We hypothesize that dimethyl Hg fluxes from the ocean to the atmosphere through polynyas and open leads in ice, and is rapidly photolyzed to MMHgCl. We also found that concentrations of MMHg in initial snowmelt on John Evans Glacier (up to 0.24 ng/L) were higher than concentrations of MMHg in the snowpack (up to 0.11 ng/L), likely due to either sublimation of snow or preferential leaching of MMHg from snow during the initial melt phase. This springtime pulse of MMHg to the High Arctic, in conjunction with climate warming and the thinning and melting of sea ice, may be partially responsible for the increase in concentrations of Hg observed in certain Arctic marine mammals in recent decades. Concentrations of MMHg in warm and shallow freshwater ponds on Ellesmere Island were also quite high (up to 3.0 ng/L), leading us to conclude that there are very active regions of microbial Hg(II) methylation in freshwater systems during the short summer season in the High Arctic.